ANDROID: GKI: power: power_supply: Add REAL_CAPACITY property

POWER_SUPPLY_PROP_REAL_CAPACITY reports the unadjusted
and unscaled battery capacity.

Signed-off-by: Anirudh Ghayal <aghayal@codeaurora.org>
(cherry picked from commit f2977772b1a49e065e34b47d264a46a0f02e61cb)
Signed-off-by: Mark Salyzyn <salyzyn@google.com>
Bug: 150789066
Change-Id: I7a016cdf89904f4d5ecbfd9b9afbd05fbfe62441